Thousands of postal workers are to be balloted for strikes in protest at plans to close sorting centres and cut jobs.
More than 3,000 members of the Communication Workers Union (CWU) in London will vote in the next few weeks on whether to launch a campaign of industrial action amid warnings that around 1,100 employees face the threat of redundancy in the capital.
London CWU official Mark Palfrey said: "Royal Mail's draconian attitude and its inability to stick to any agreements is nothing short of disgraceful. This has left the CWU with no other option than industrial action."
The ballot result is due on May 23.
A Royal Mail spokesman said: "After a nine-month consultation with the CWU - which was extended twice at the union's request - Royal Mail announced in March a £69 million investment in its operations in the capital and plans to close two of seven mail centres in London with the loss of 751 jobs.
"The company is confident all of the changes can be handled on a voluntary basis and it has a very good track record in doing so.
"A full customer service continues as normal in London and everywhere else in the UK."